This invention relates generally to electric connectors and, more particularly, to an improved terminal assembly for connecting the bus conductor of a circuit braker or other device to an external line cable.
As is well known in the art, circuit breakers and similar devices such as switches require a reliable and economical terminal means for connecting the bus conductor of the circuit interrupter or switch to an electric cable which comprises part of the line circuit which is being protected from overload conditions or must be isolated for other reasons. Prior art terminal structures generally consisted of a metal lug that had a pair of screws disposed in tapped holes provided in the top and bottom walls of the lug and adapted to engage a tapped hole in the inserted end portion of the bus conductor to secure the latter to the lug and then permit the inserted end of the line cable to be clamped in overlapping electrical contact with the bus conductor when the second screw was tightened. In other prior art connector arrangements a terminal lug (or clip) was mounted on top of the bus conductor by means of a screw that passed through a hole in the bus conductor and engaged a tapped hole in the terminal lug, thus fastening the bus conductor to the bottom of the terminal lug.
In another prior art design, the terminal lug consisted of a U-shaped body member having a hinged L-shaped support that was fitted with a locking screw and rotatable retaining means which permitted the line conductor to be inserted downwardly into the body member and then clamped in place against the bus conductor anchored at the bottom of the body member. A terminal assembly of this type is disclosed in U.S. Pat. No. 3,559,156 issued Jan. 26, 1971 to K. R. Coley.
In accordance with a more recent development in the art, the terminal lug is coupled to the apertured end of the bus conductor by a U-shaped retaining clip that is force-fitted over the end of the bus conductor and bottom wall of the terminal lug after the bus conductor has been inserted into the lug and slipped over a boss that protrudes from the bottom wall of the lug and engages the opening in the bus conductor. A clip-connected terminal lug assembly which embodies this design and includes a terminal screw that extends through the top wall of the lug and forces the inserted end of the electric cable against the clip-anchored bus conductor is disclosed in U.S. Pat. No. 3,891,298 issued June 24, 1975 to N. Yorgin et al.
While the prior art connector structures and terminal assemblies were satisfactory from the standpoint of effecting the electrical juncture of the bus conductor and line cable by mechanical means which permitted the line cable to be connected and disconnected from the bus conductor of a circuit interrupter or switch which has been mounted on a control panel or the like, they had various inherent disadvantages from both a functional and cost standpoint. The use of screws to fasten a tapped bus conductor to the inner or outer face of the bottom wall of the terminal lug, for example, made it difficult to make such a connection--particularly when a molded-case type circuit breaker is involved and the terminal assembly is recessed within a portion of the breaker case and there is very little room for threadably coupling the screw to both the terminal lug and bus conductor. The use of metal clips or nuts inside the terminal lug to anchor the bus conductor to the lug interfered with or prevented clamping the inserted ends of the bus conductor and electric cable in direct contact with one another with the result that high resistance areas in the terminal connection sometimes occurred which were undesirable from a functional and safety standpoint. Fastening the bus conductor to an exterior part of the terminal lug by means of a screw or other member is also undesirable since this arrangement makes the lug a current-carrying part of the electric circuit.
Another disadvantage encountered with the use of terminal assemblies having screws which engaged a tapped hole in the bus conductor was the necessity of using bus conductors which were thick enough to provide a sufficient number of threads to avoid stripping them during the conductor-coupling operation. The prior art terminal lugs also have openings of such configuration that the cable conductor can gradually loosen from its clamped position after it has been heated and cooled a number of times, particularly when the cable is of the multi-strand type.
The provision of a terminal assembly which would permit the bus conductors of circuit interrupters, switches and similar devices to be clamped directly to the line cable in a simple and expedient manner with a minimum number of parts that not only eliminate the need for a tapped hole in the bus conductor but ensures that the line cable remains firmly clamped in direct positive contact with the bus conductor under both normal and adverse operating conditions would constitute a useful improvement in the art from both a cost and quality standpoint.